Key Terms
DEFINITION
Metabolic rate = rate at which the body uses food energy. Basal metabolic rate (BMR) = metabolic rate at complete rest.
Unit
Watt (W). 1 W = 1 J/s.
Holding a heavy object still
Displacement = 0, so W = 0. Carrying an object horizontally at constant speed: force is upward, displacement is horizont
Positive work
Force and displacement point the same direction. Negative work: force and displacement point opposite directions.
Two ways to find net work
1. Find the net force first, then W_net = F_net x d x cos(theta).
Positive net work
Object speeds up (KE increases). Negative net work: object slows down (KE decreases).
Change in gravitational PE
Delta(PE) = m g delta(h)
When an object falls freely (no friction)
Loss of PE = Gain in KE m g h = (1/2) m v^2
Examples
Gravity, spring force. Non-examples: friction, air resistance.
PE of a spring
PE_spring = (1/2) k x^2
When ONLY conservative forces act
ME_initial = ME_final KE_i + PE_i = KE_f + PE_f
Primary example
Friction. The longer the path, the more work friction does.
LAW OF CONSERVATION OF ENERGY
Total energy is constant in any process. Energy changes form or transfers between systems; it is never created or destro
Full equation
KE + PE + W_nonconservative + OE = constant Where OE = all other forms of energy (chemical, thermal, electrical, etc.)
Also expressed as
P = F v (useful when force and velocity are known directly, no need to calculate work separately)